Dyeing conventional and microfiber polyester with disperse dyes
Uddin, Md Zulhash
The small radius of microfibers causes some problems with the dyeing process and colorfastness of the dyed fabrics. In this study, we examine the high temperature (130 deg C) dyeing, light-fastness, and wash-fastness characteristics of seven different disperse dyes on both conventional (5.5 decitex per filament) and microfiber (0.56 decitex per filament) polyester. We analyze regression equations of build-up curves for different disperse dyes in 1/1 standard depth dyeings. Using a spectrophotometer, we determine K/S values at the appropriate lambda^sub max^ for each dye. The extent of dye exhaustion is expressed in terms of color strength (K/S) using the Kubelka Munk equation. The results of our investigation show that polyester microfibers consume two to three times more disperse dye than conventional polyester fibers. The light-fastness level of polyester microfibers is less than conventional polyester. All the disperse dyes exhibit excellent wash-fastness for both conventional and microfiber polyester.
Dye consumption in a dyeing process and the colorfastness characteristics of the dyed goods are very important factors for quality products in the textile industry. The decade of the nineties has seen major innovations in the U.S. textile industry. A prime example has been the arrival of polyester (PES) microfibers , which are becoming more important in the textile trade. A microfiber is defined as a fiber or filament with a linear density of approximately 1 decitex or less, where decitex is the mass in grams of 10 Km of filament [4, 6, 15]. The development of PES microfibers has provided opportunities to produce a new generation of fibers and fabrics with totally novel characteristics [4, 5, 11, 15].
Conventional and microfiber PES are exclusively dyed with disperse dyes [1, 2]. However, despite all the exciting possibilities of PES microfibers, they have some difficulties with dyeing and colorfastness. McGregor et al.  reported that the effect on the dyeing rate of a stagnant solution layer surrounding the fibers is greater when dyeing microfibers. Nakamura et al.  studied the sorption isotherms and dyeing rates of disperse dyes on polyester microfibers from water. Kobsa et al.  demonstrated an optical ray tracing, luster prediction computer model to explain the reduced dye yield of microdenier yams.
PES microfibers have a high specific surface area [4, 11, 12]. Leadbetter et al.  reported percent dye consumption figures by microfibers, which they calculated using the Fothergill rule. Partin  also used the path length equation to determine percent dye consumption when comparing fabrics containing fibers with different yam counts. However, detailed studies on the relation between the amount of dye in the fiber and the visual color depth and colorfastness characteristics of the microfibers are insufficient. On the other hand, no papers have dealt with the regression analysis of 1/1 standard depth dyeing on microfibers.
In this paper, we investigate high temperature (130 deg C) dyeing, light-fastness, and wash-fastness on (1/1 standard depth dyeings) both conventional (5.5 decitex per filament) and microfiber (0.56 decitex per filament) PES. We analyze regression equations of build-up curves for different disperse dyes in 1/1 standard depth dyeings. We examine and compare the dye consumption figures, light– fastness, and wash-fastness characteristics for conventional and microfiber PES for seven different disperse dyes. The objectives of the research are to investigate the influence of fiber fineness (conventional and microfiber PEs) on the color yield of different disperse dyes, and to examine and compare light-fastness and wash-fastness characteristics for conventional and microfiber PES dyed with different disperse dyes.
We used 100% PEs fabrics in this investigation. Pretreated conventional [167 decitex warp and weft yam (5.5 decitexpf)] and microfiber [76 dtex warp (0.56 decitexpf) and 100 dtex weft (0.56 decitexpf) yarn] woven fabrics were kindly supplied by Dupont (England). Seven different disperse dyes (ICI Ltd., England) were used as obtained. The names of the dyes are given in Table I.
For the high-temperature (HT) dyeing, disperse dyes were ready-made in solid form and dye dispersions were made by adding water and buffer solution just before dyeing. All dyeings were carried out in sealed, stainless steel dyepots of 100 cm^sup 3^ capacity housed in a Mathis labomat laboratory– scale dyeing machine. There were twelve dyebath arrangements. We used 3 g of fabric in each bath. The fabrics were dyed at 130 deg C for 60 minutes in 0.25 to 20% dye (twelve dye concentrations) using a 20:1 liquor to goods ratio at pH = 5. Dyeing began at 60 deg C, and the bath temperature rose at a rate of 1 deg C a minute. For cooling, the bath temperature decreased at the same rate. After dyeing, we performed a reduction cleaning treatment with 1 g/L Matexil DN-VL 200, 2 g/L sodium bisulfite, and 4 ml/L caustic soda (66 deg Tw) using a 50:1 liquor to goods ratio at 70 deg C for 30 minutes. After thoroughly rinsing, samples were soaped with 1 g/L Sandoclean Pc using a 50:1 liquor to goods ratio at 50 deg C for 30 minutes, then rinsed thoroughly, dried at ambient temperature, and used for color measurements.
For the 1/1 standard depth dyeings, seven different disperse dyes were applied on conventional and microfiber PES at identical dyeing conditions (130 deg C for 60 minutes) and various dye concentrations (Table I) to achieve the same visual shade depths. Polynomial third-degree regression equations of build-up curves with K/S = 6 units (because of uniform dye uptake in this region for both conventional and microfiber PES) were used for the analysis. Figure 1 shows the method used to calculate concentrations (% owf) of Disperse Red C-4G 150 (d5) on conventional and microfiber PES to achieve 1/1 standard depth dyeings. The regression equations of dye build-up curves on conventional and microfiber PES are shown in Figure 1. For K/S = 6, ie., Y = 6 units, the dye concentrations on conventional and microfiber PEs to achieve 1/1 standard depth dyeings are 0.535 (% owf) and 1.641 (% owf), respectively, as shown in Figure 1. We used the same method for other dyes to calculate concentrations (Table I) to achieve 1/1 standard depth dyeings.
For the color measurements, the reflectance values of the dry, reduction cleaned, and dyed fabrics were measured (from 400 to 700 nm at 10 nm intervals) using a Macbeth MS 2020 spectrophotometer (Kollmorgen, USA) interfaced to a Digital PC 100 personal computer under a D^sub 65^ illuminant using a 10 deg standard observer with specular component excluded and uv component included. Each dyed sample was folded twice so that a total of four layers of fabric were presented to the spectrophotometer. An average of four measurements per sample was taken. The corresponding K/S values and CIE L*, a*, b*, C*, and h deg coordinates were calculated at the appropriate lambda^sub max^ of each dye from the reflectance values. Apparent color strength was expressed as KIS using the Kubelka-Munk equation, K/S = (1 – R)^sup 2^/2R, where R is the reflectance of dyed fabric at the maximum absorption wavelength of dye, K signifies the absorption coefficient, and S is the scattering coefficient. We compared the apparent color strength of dye d4 (anthraquinone) with other dyes. The apparent relative color strengths of dyes d1, d2, and d3 (heterocyclic benzodifuranone) were less than d4 and the dyes d5, d6, and d7 (mono azo) showed higher apparent relative color strengths compared to dye d4.
For the colorfastness determinations, we tested light– fastness in a xenon-arc fading lamp tester. The specimens (1/1 standard depth dyeings) and references were mounted in exposure masks and exposed to light according to AATCC Test Method 16-1990: Colorfastness to Light, Water Cooled Xenon-Arc Lamp Continuous Light. A black panel temperature of 63 deg +/- 1 deg C (145 deg +/- 2 deg F) and 30 +/- 5% RH, with borosilicate inner filters and soda lime outer filters was used to simulate the range of spectral energy that passes through ordinary window glass. Exposure periods were controlled by a xenon reference fabric (acid dyed wool fabric with a linear fading rate). For wash-fastness, the 1/1 standard depth dyeings were subjected to an ISO C06/C2 wash test ; shade changes of the original colored specimens, together with the extent of staining of the adjacent fabrics, were assessed using the appropriate grey scale . We analyzed five samples in order to get every result.
Results and Discussion
Table I shows the list of the disperse dyes and their concentrations on conventional and microfiber PES for identical shade depths. We calculated each dye concentration on conventional and microfiber PES, based on its build-up curves. We analyzed polynomial third-degree regression equations and regression correlation co-efficients (R^sup 2^) of build-up curves of different disperse dyes to calculate (by a computer XL program) required dye concentrations (Table I) on conventional and microfiber PES for identical shade depths. The details of the method are shown in Figure 1.
We compared the color yields of different disperse dyes in Figures 2-8 on conventional and microfiber PES at 130 deg C for 1 hour. Figure 2 shows the color yields of Dispersol Red C-BN SF. A higher K/S value indicates more dye absorbed into the fibers and vice versa. The apparent color strength continues to increase with increasing initial dyebath concentration until there is > 15% of dye on both the fibers, and it is then saturated. The rate of color build-up suggests a similar trend for both conventional and microfiber PES. Dye consumption on PES microfibers must be 2.63 times (Table I) that for conventional PES to produce visually the same shade depth.
Figure 3 displays the color yields of Dispersol Brilliant Red DSF. The apparent color strength continues to increase up to 15% initial dyebath concentration and is then saturated on both conventional and microfiber PES. There is a crossing at 8% dye concentration, indicating a considerable difference in initial color yields and very little difference in final color yields between conventional and microfiber PES. The rate of color build-up demonstrates a small difference between conventional and microfiber PES. Dye consumption on PES microfibers is 2.05 times (Table I) that of conventional PEs to produce visually an equal shade depth.
Figure 4 shows the color yields of Dispersol Brilliant Scarlet DSF. The apparent color strength continues to increase up to 20% initial dyebath concentration, and the rate of color build-up also indicates a similar trend for conventional and microfiber PES. Dye consumption on PES microfibers is 2.55 times (Table I) that of conventional PEs to produce visually the same shade depth.
Figure 5 shows the color yields of Disperse Red B-2B 200, which also displays a crossing at 6% dye concentration. The apparent color strength continues to increase very slowly up to 15% initial dyebath concentration, and is then saturated on both fibers. Dye consumption on PES microfibers is 2.68 times (Table I) that of conventional PEs to produce visually an equal shade depth.
Figure 6 demonstrates the color yields of Disperse Red C-4G 150, indicating a crossing at 8% dye concentration. In this case, there is also a considerable difference in initial color yields and very little difference in final color yields between conventional and microfiber PES. The rate of color build-up is more irregular on PES microfibers than on conventional PES. Dye consumption on PES microfibers is 3.07 times (Table I) that of conventional PES to produce visually the same shade depth.
Figure 7 displays the color yields of disperse Rubine C-B 150, which exhibits a crossing at 6% dye concentration and then is saturated. In this case, the rate of color build-up is also more irregular on PEs microfibers than on conventional PEs. Dye consumption on PES microfibers is 2.80 times (Table I) that of conventional PES to produce visually an equal shade depth.
Figure 8 shows the color yields of Disperse Red D-B, which also displays a crossing at 9% dye concentration. The rate of color build-up is more irregular on PEs microfibers than on conventional PES. Dye consumption on PES microfibers is 2.59 times (Table I) that of conventional PES to produce visually the same shade depth.
From the apparent relative color strengths of different disperse dyes, we calculated the range of dye consumption on PES microfibers, which was two to three times that of conventional PES fibers. Because the polymer used in the microfibers is the same as that employed in the conventional fibers, these observed differences in the color strength (K’S) of dyeings on conventional and microfiber PES could be attributed to the greater surface area and light reflection of the dyed microfibers. Figures 2-8 reveal that the shape of the build-up curves is similar for both conventional and microfiber PEs for each dye. Furthermore, each of the seven dyes under investigation exhibits very good build-up characteristics on conventional fibers in contrast to the medium build-up characteristics on microfibers.
The PES microfiber (0.56 dtexpf) is 9.8 (5.5/0.56) times finer than conventional PES (5.5 dtexpf), so the same cross– sectional area of PES microfiber yarn contains more fibers than a conventional PES yam. As a result, the surface area of PES microfibers is greater than conventional PES fibers for the same cross-sectional area. Because of this increased surface area, microfibers require more dye than conventional PES fibers to attain a given shade depth.
There may be many causes for variations in dye consumption from dye to dye. The color yields of the disperse dyes may be influenced by some other factors such as fiber cross-section and morphology , size particles, and chemical structure of the dyes . Fiber morphology (i.e., the arrangement of polymer molecules within the fiber), crystallinity, amorphousness, and amorphous areas of the fiber play important roles in disperse dyeing. Sakai et al.  reported that saturation dye uptake of Disperse Red 15 by polyester film increases with the film’s crystallinity. McDowell et aL  reported that saturation dye uptake of Disperse Red 15 by a biaxialy drawn polyester film with a high degree of crystallinity at 120 deg C is higher than that of amorphous film.
We used seven disperse dyes to examine and compare light-fastness and wash-fastness characteristics among monoazo, heterocyclic benzodifuranone, and anthraquinone dyes, then magnified the difference in performance on conventional and microfiber PES. Table II shows the comparison of light-fastness levels between conventional and microfiber PES dyed with different disperse dyes. PES microfibers exhibit less light-fastness than conventional PES for all dyes. The rating range on conventional PES is from 5 to 7-8, and the range on PEs microfibers is from 3-4 to 7. The rating differences are 0.5, 1, and 1.5 units between conventional and microfiber PES for the different disperse dyes. The range difference is 0.5 to 1.5 units. The finer fiber shows less light-fastness than the coarser fibers. The lightfastness characteristics of disperse dyes may depend on some other factors such as fiber cross-section, chemical structure of the dye, chemical nature of the substituents, fabric construction, etc. Aspland  reported that the general structure of the monoazo disperse dyes is largely based on the parent compound aminoazobenzene. We see from Table II that the anthraquinone disperse dye (d4) exhibits the maximum light-fastness.
Table III shows a comparison of wash-fastness levels for conventional and microfiber PEs dyed with different disperse dyes. Wash-fastness ratings are excellent and the same (5) for both conventional and microfiber PES for all the disperse dyes. Each dye exhibits the same results. This finding can be explained in terms of the reduction cleaning and the dye properties. It may be that all the surface dye particles of conventional and microfiber PEs were removed after the reduction cleaning and soaping treatment. Also it may be that the dyes have good resistance to sublimation. Leadbetter et aL  reported that disperse dyes, traditionally used to dye conventional polyester and its associated blends, can produce unacceptable levels of wash-fastness on microfibers. Partin  proposed that the wash-fastness of microfibers is not be a major problem with proper reduction cleaning, finishing, and heat treatments.
We have discussed the color yields, light-fastness, and wash-fastness characteristics of different disperse dyes on both conventional and microfiber PEs. Application at 130 deg C and pH 5 yields optimum color strength for all the disperse dyes on both conventional and microfiber PFs. The excellent build-up characteristics on conventional PES for all disperse dyes contrast with the medium build-up characteristics on microfiber PES. From the results of our investigation, we can conclude that PES microfibers need to consume two to three times more disperse dye than conventional PES fibers to achieve identical visual shade depths. The light-fastness rating of PES microfibers decreases from 0.5 to 1.5 units compared to conventional PES fibers for the same visual shade depth. Conventional and microfiber PES have the same and excellent wash-fastness for equal shade depth if reduction cleaned and soaped properly.
We thank Prof. Dr. Paul Kiekens (Department of Textiles, University of Ghent, B-9052 Zwijnaarde, Belgium) for his fruitful disscusion and valuable suggestions to this work. This work was partly supported by Grant-inAid for COE Research (10CE2003) by the Ministry of Education, Science, Sports and Culture of Japan.
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MD. ZULHASH UDDIN, MASASHI WATANABE, HIROFUSA SHIRAI, AND TOSHIHIRO HIRAI(1)
Faculty of Textile Science and Technology, Shinshu University, Ueda-shi 386-8567, Japan
(1)To whom correspondence should be addressed: tel: +81-268– 215405, fax: +81-268-21-5391, e-mail: firstname.lastname@example.org
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